This application discloses an invention which is related, generally and in various embodiments, to thin foil encapsulated insulation assemblies.
In various technologies, effective insulation for providing heat retention is an important design component. One example of a technology in which effective insulation is desired is the field of exhaust after-treatment systems for treatment of harmful exhaust emissions from internal combustion engines. Typical exhaust after-treatment systems are configured to reduce the level of undesirable exhaust byproducts such as nitrogen oxides. Accordingly, conventional exhaust after-treatment systems include a decomposition tube and fitting for an injector designed to inject a urea based diesel exhaust fluid or reductant, which is capable of decomposing into gaseous ammonia and carbon dioxide in the presence of exhaust gas within the tube under certain conditions. After exiting the decomposition tube, exhaust gas flows through a selective catalytic reduction (SCR) system where the ammonia reacts with nitrogen oxides to produce nitrogen and water. The catalytic conversion of nitrogen oxides is highly dependent on temperature, making heat retention through effective insulation a critical design requirement for decomposition tubes.
Insulating both the decomposition tube and the junction with injector module is possible using double walled tubes with insulation disposed in the annular space between an inner tube and an outer tube. Such a junction typically includes the decomposition tube with an integral injector tube to which an injection flange is joined for mounting the injector module. Insulating the junction between the decomposition tube and the injector tube is possible using relatively thick outer tubes and insulation housings that can be welded together at the junction to provide the necessary support and structural rigidity required to transfer loads between the decomposition tube and the injector tube. Nonetheless, double-walled tubes are expensive and add weight to the overall system. To avoid using double-walled systems, foil is used to surround the tube insulation on both the decomposition tube and the injector tube, but little or no insulation is used at the junction between the decomposition tube and the injector tube because there is no outer tube on which to support an insulated junction housing.
Thus, there is a need for a tube junction that can be insulated at relatively low cost and maintain light weight of the assembly.